The public telephone network provides an enhanced service to telephone customers wherein telephone customers subscribing to the service may receive information identifying the telephone number of a telephone station calling the telephone customer. The enhanced service, called Automatic Number Identification Delivery Service, forwards the telephone number of the calling telephone station over the public telephone network to the called telephone customer. In operation, a user of a calling telephone station dials a predetermined telephone number, such as an 800 telephone number, assigned to a telephone customer having subscribed to 800 enhanced telephone service. A local exchange carrier telephone company serving the calling telephone station transmits the dialed 800 telephone number and the telephone number assigned the calling telephone station to an originating screening office of the public telephone network.
On each incoming 800 call, the originating screening office temporarily stores the calling telephone number and formulates a query data message identifying the dialed 800 and calling telephone area code numbers that is transmitted over a data link to a telephone network centralized data base, such as a network control point. The network centralized data base translates the received 800 telephone number into a North American Numbering Plan destination telephone number which is transmitted as a reply data message over a data link back to the network originating screening office. Upon receipt of the reply data message, the originating screening office establishes a call connection between the calling telephone station and the called telephone station in accordance with the destination telephone number over the telephone network and transmits the stored calling telephone number to the called customer.
A problem arises with the current system in that for each dialed 800 telephone call incoming to the originating screening office a query data message must be formulated and transmitted to the network centralized data base. In addition, a reply data message must be generated by the network centralized data base and returned to the originating screening office before the connection can be established with the called telephone customer. The time spent in formulating the data messages and transmitting them between the originating screening office and the network centralized data base greatly increases the setup time required to establish the call connection. The increase of the call connection time creates another problem in that it reduces the number of incoming 800 telephone calls that can be handled by the network originating screening offices.